1. Field of the Invention
This invention relates in general to electrical cable, and in particular to electrical cable for use with submersible pumps in oil and gas wells.
2. Description of the Prior Art
Cross-linked polyethylene has been used for many years as an insulator for electrical conductors. The cross-linked polyethylene provides a very stable insulator which is fairly inexpensive and is resistant to deterioration when subjected to elevated temperatures. Cross-linked polyethylene, however, has not been used extensively in submersible well pump applications because of its tendency to degrade when subjected to oil and other liquid hydrocarbons which are commonly found in oil and gas wells.
In the past, electrical cables used for submersible well pumps have primarily been constructed with polypropylene or EPDM (ethylene-propylene diene monomer) insulation. Polypropylene is readily available, has good dielectric properties and is fairly inexpensive, however, polypropylene is subject to deterioration when subjected to the high temperatures found in some oil and gas well environments. Normally, the maximum temperature polypropylene is able to withstand is about 205 degrees Fahrenheit. This restricts the use of polypropylene as an insulating material for electrical submersible pump cables to low temperature wells. EPDM insulation, on the other hand, does not deteriorate when subjected to high temperatures, even up to 400 degrees Fahrenheit. The EPDM insulation, however, is prone to swelling with exposure to hydrocarbon well fluids and is relatively expensive. During extrusion, EPDM is normally cured in a steam tube which is a fairly slow process.
It would be beneficial to have an electrical cable insulation for a submersible well pump which is stable under higher temperatures than polypropylene, will not swell or deteriorate when subjected to exposure to well fluids such as oil and other liquid hydrocarbons, and is less expensive than EPDM.